Solvent extraction process

ABSTRACT

A PROCESS FOR THE SEPARATION OF AROMATIC HYDROCARBONS FROM SATURATED HYDROCARBONS USING A SOLVENT COMPRISING A SUCCINIMIDE IN WHICH A FEED STOCK CONTACTS THE SOLVENT AT SOLVENT EXTRACTION CONDITIONS. THE RESULTING RAFFINATE AND EXTRACT PHASES ARE SEPARATED. THE EXTRACT PHASE IS THEREAFTER SUBJECTED TO TREATMENT TO REMOVE AROMATIC HYDROCARBONS THEREFROM. THE SOLVENT MAY BE RECYCLED TO THE PROCESS FOR CONTINUOUS USE.

United States Patent 3,689,405 SOLVENT EXTRACTION PROCESS Armand J. De Rosset, Clarendon Hills, 11]., Richard C.

Wackher, Forsyth, Mo., and Stephen 'N. Massie, Palatine, Ill., assignors to Universal Oil Products Company, Des Plaines, Ill. No Drawing. Filed May 3, 1971, Ser. No. 139,972

Int. Cl. C07c 7/10; Cg 21/00 US. Cl. 208326 8 Claims ABSTRACT OF THE DISCLOSURE A process for the separation of aromatic hydrocarbons from saturated hydrocarbons using a solvent comprising a succinimide in which a feed stock contacts the solvent at solvent extraction conditions. The resulting rafiinate and extract phases are separated. The extract phase is thereafter subjected to treatment to remove aromatic hydrocarbons therefrom. The solvent may be recycled to the process for continuous use.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a solvent extraction process in which aromatic hydrocarbons are separated and concentrated from feed stock containing both aromatic and saturated hydrocarbons.

Description of the prior art References which relate to the process of this invention include Belgian Pat. No. 744,589, published on July 20, 1970, and West German application No. 1,545,225, filed on Jan. 30, 1965, and published on July 23, 1970. The above foreign references refer to the use of certain heterocyclic compounds which can be used as solvents in an extraction process.

SUMMARY OF THE INVENTION Solvents which can be used in the process of this invention are generally derived from a general class of materials defined as succinimides. The succinimides may be prepared conveniently by heating succinic acid, succinic anhydride or succinate esters with ammonia. The general structure of succinimide is shown in Equation 1 below:

can be utilized as solvents in the process of this invention. The R R and R substitutional groups are selected from hydrogen or an alkyl group of carbon number less than about 5.

Specific examples of succinimide type compounds which are included in the above formulas are succinimide, N-methylsuccinimide, N-Z-dimethylsuccinimide, 2-methylsuccinimide, 2,3-dimethylsuccinimde, etc. In some instances, the melting points of the above compounds are high enough so that high temperatures must be used in the process in order to allow a liquefied operation to take place. In order to substantially reduce the probabilities of high melting points of the succinimides it is generally preferred that in instances where R; and R are hydrogen that R must be an alkyl group of four carbons or less in order to obtain a low melting point of the succinimide compound. Substitution at the nitrogen position may also be utilized to improve the solubility of hydrocarbons in the solvent.

The solvent which can be used in the process of this invention are preferably in a liquefied form and may be in admixture with quantities of other compounds including water or organic compounds to enhance the solvents selectivity in extracting aromatics from the feed mixture. Specifically, the succinimide material may be diluted with various quantities of water, glycols including ethylene glycol and diethylene glycol, 4-methyl-l,3 dithiolane-l,1, 3,3-tetraoxide, M-methyl-Z-pyrrolidone, 1,3-propane sultone, the sulfolanes or other organic compounds. The diluents should be soluble with the solvent and should enhance the extraction of aromatic hydrocarbons by the succinimide solvent. The quantity of the diluents which may be present in'the solvent can vary anywhere from a few percent up to about 15 to 50 wt. percent of the solvent and may include both water and organics. Optimum quantities of the various inert diluents can be found by experimentation.

Solvent extraction conditions include liquid phase operations at temperatures anywhere from above about ambient temperatures up to and including 250 C. In many instances it is possible to operate in a liquid phase condition at a temperature below the melting point of the particular solvent used because of the depression of the solvents freezing point by the inert diluent. Pressures should be maintained to enable liquid phase operations to take place.

Various contacting means can be utilized in the process of this invention to effect a solvent extraction. Rotating disc contacters can be used for solvent and feed stocks to contact one another in a countercurrent manner to effect intimate mixing. The extraction operation can be performed in a continuous type operation or in a batchwise separation. Specifically, feed stock and a solvent mixture can be allowed to contact each other for a certain period of time after which extract and rafiinate phases are separated. Saturated components can be recovered from the rafiinate phase and the aromatic component from the extract phase.

In many instances, the solvent which may be dissolved in the raflinate phase may be removed from the raflinate phase by fractionation or by water-washing in order to prevent undue solvent losses in the process. The extract phase can be passed into a fractionating column so the solvent may be separated from aromatic components. Diluents which are present in the solvent can also be separated from the solvent and aromatic components in the fractionator. Typical fractionation schemes include extractive distillation followed by a simple fractionation step in order to separate the extract phase from the solvent material. The solvent can be reused and passed into the extraction portion of the process after being mixed with the proper quantity of the organic diluent or water if either or both are desired to be used to enhance aromatic separation. In some instances the solvent may require further treatment to remove impurities derived from the feedstock or from the breaking down of solvent materials.

Feed stocks which can be used in the process of this The solvents used all contained at least one form of a succinimide or a derivative and are specifically described in Table 11 below:

TABLE II.SOLVENT DESCRIPTIONS invention include straight run gasolines and certain com- Weight ponents from reformmg, catalytic cracktng, hydrocrack percent Description mg, or isomertzation processes. Spec1fica1ly, the feed stocks utilized in the process of this invention include ffi 100 0 Succinimide both aromatic hydrocarbons and saturated hydrocarbons. IIIIIIII: 7510 Sqccinimide: The aromatics contemplated as feed stocks include monomethylene glywland poly-nuclear aromatics. Specifically aromatics which A3 75.0 Succinimide. are contemplated as being components present in the feed dithmlemlili3i3'ttteltdei stock of the process of this invention include benzene, A4 50.0 Succinimide. toluene, ethylbenzene, para-xylene, meta-xylene, ortho- N'methyl'z'pytmlidmexylene, isopropylbenzene, normal propylbenzene, the di- A5 50.1 Succinimlde. ethylbenzenes, the trimethylbenzenes, the butylbenzenes, lfihmpane Sulttme the methylpropylbenzenes, tetramethylbenzenes, the naph- B 100.0 N-methylsuccinimide. thalenes including alkyl derivatives thereof. Saturated C 100-0 zmethylsuwmmldehydrocarbons include straight or branched chain paraffins eyelpafaffihs hevlhg from 51X P to tyearbfm The Water content of the raffinate and extract phases atoms P moleeule- The eyelopafaffihs fl be was normalized out of the calculations. Water was added eluded as part of the feed stocks of th1s 1nvent1on 1nclude t th l t i t t 1 6 as t f h normal t i h y y p eyeloheXflne and the alkyl deriveprocedure since water had been found to enhance many tlves theteotother Components h as Olefihs solvents abilities to selectively concentrate aromatics in olefins may be present as mlnor const1tuent of the feed an extract h 15 Preferred that y not be 111 y hlgh COII- The selectivities were found by calculating the ratio of centratlon and $hu1d he less than about Volume P the weight ratios of benzene over methylcyclopentane in cent of the feed stock in order to reduce their undesirable h extract d raflinate phases respectively, I h case Influences Oh h p a selectivity greater than unity was found which indi- The aromatics. branched and stfelght ehflllled p ffi i cated that each solvent would selectively concentrate aroand the cycloparaffins can vary 1n concentrauon 1n a i i h extract h feed stock dependlhg Oh the Source of the feed StOek- In tests 1, 6, 7 and above, a single solvent was used to is 2 3 4 and 5 succinimide PREFERRED EMBODIMEN concemtaiaammatws 111 a t TS EXAMPLES or a der1vat1ve compound was m1xed w1th another solvent In this example a succinimide material w d t to determine whether or not the specific comblnatlon illustrate the process of this invention. The apparatus would offer an g us s p i used consisted of a sealed bomb which could sustain a The above examples are Offered as speclfie emhodlments moderate amount of pressure and temperatures up t of the process of th1s invention and are not to be taken about 200 C. The bomb was filled with a feed to k nas an undue limitation on the scope of the attached claims. sisting of about 80 vol. percent methylcyclopentane and 40 A broad embodiment of the present mvent1on relates 20 vol. percent benzene and the desired solvent and then to a Process for the Separetlon 0f eromatle hydrocarbons shaken to cause intimate mixing of both the feed and from a mixture of aromat1c and saturated hyd a s solvent materials. The bomb was then placed in a conwhich process comprises contactmg sa1d mixture w1th a stant temperature bath maintained at 121 C. The bomb solvent containing a succmimrde or derivative thereof at was occasionally shaken after the contents of it had conditions to etfect the concentration of the aromatic by reached 121 C. After about one hour at 121 C. the said solvent and recovering the aromatic from the solvent. contents of the bomb were sampled by drawing off We claim as our invention: rafiinate (upper) and extract (lower) phases of liquid. 1. A process for the selective extraction of an aromatic The results of the experiment are shown in the Table I hydrocarbon from a feed stock containing aromatic and below: saturated hydrocarbons which process comprises contact- TABLE I.-TEST RESULTS Test Solvent type..:-.:.;::.;.-:.': A1 A2 A3 A4 A5 B C Solvent mixture:

Solvent, grams 85.05 100. 04 98.00 05.00 98.04 84.10 102. 49 Water, grams 15.57 2.04 2.10 5.03 1.97 9. 29 Solvent, weight percent. 84.5 98.0 97.9 95.0 98.0 90.1 100.0 Water, weight percent... 15.5 2.0 2.1 5.0 2.0 9.9 Feedstock:

Benzene (BZ),grams 0.30 5. 04 0.15 7.50 0.21 7.51 5. 40 Methylcyclopentane (MOP), 25.52 24.04 23.85 27.42 26.13 28.61 22. 26

rams. Bz weight percent 19.8 19.8 20.5 21.6 19.2 20.8 19.7 MCP,weigl1t; percent 80.2 80.2 79.5 78.4 80.8 79.2 80.3 Rafllnate phase sample:

Solvent, grams 0.19 0.13 0.34 0.20 0.05 0.75 132, grams 0.75 0.77 1.10 0.05 1.50 0. 47 0.80 MCP,grams 4.32 4. 63 7.25 5. 96 8.71 3.53 7.81 Solvent, weight percent 3.6 1. 5 4. 9 1. 9 1. 2 8. 0 Bz,weight percent.... 14.2 14.3 13.9 9.4 14.4 11.6 8.5 MCP,weight percent- 82.2 85.7 84.6 85.7 83.7 87.2 83.5 Extract phase sample:

Solvent, grams 73. 28 29.14 09.37 48.57 57.30 70.63 64. 78 137., grams 1.30 0.72 1.42 4.40 1.18 3. 51 2.45 M01, ams 0. 50 0.48 0.72 2.21 0.04 4. 00 5.20 Solvent, weight percent. 97.6 96.0 97.0 88.0 96.9 89.8 89.4 Bz, weight percent 1. 7 2. 4 2.0 8.0 2. 0 4. 4 3. 4 MCP,weightpercent-.- 0.7 1.6 1.0 4.0 1.1 5.8 7.2 Selectivity (BZ/MOP) 15.2 0.0 12.0 4.0 10.8 5.0 4.5

ing said feed stock with a solvent containing a material having the formula:

wherein R R and R are selected from the group consisting of hydrogen or an alkyl group of carbon number less than 5, at solvent extraction conditions to effect the selective extraction of aromatic hydrocarbons by the solvent, recovering solvent and said selectively extracted aromatics and recovering said aromatics from said solvent.

2. Claim 1 further characterized in that said aromatic hydrocarbons contained from about 6 to about 15 carbon atoms per molecule.

3. Claim 1 further characterized in that said saturated hydrocarbons have from about 6 to about 20 carbon atoms per molecule.

4. Claim 1 further characterized in that said saturated hydrocarbons are cycloparaffins.

5. Claim 1 further characterized in that R R and R are hydrogen.

6. Claim 1 further characterized in that R; is a methyl group and R and R are hydrogen.

7. Claim 1 further characterized in that R is a hydrogen and R and R are methyl groups.

8. A process for the selective extraction of aromatic hydrocarbons selected from the group consisting of benzene, toluene, the xylenes and ethylbenzene from a feed stock containing aromatic hydrocarbons and saturated hydrocarbons which process comprises contacting feed stock with a solvent comprising material having the formula:

H H+----c-H 0:0 :0

N H611 H at solvent extraction conditions to eifect the selective extraction of said aromatic hydrocarbons by said solvent, recovering solvent and said selectively extracted aromatics and recovering said selectively extracted aromatics from said solvent.

References Cited UNITED STATES PATENTS 3,120,487 2/1964 Norton et a1 260-674 3,565,794 2/1971 Pigache 260-674 3,617,535 11/1971 Weitz et a1. 208-326 DELBERT E. GANTZ, Primary Examiner C. E. SPRESSER, J R., Assistant Examiner U.S. Cl. X.R. 

